In the field of membrane transport, studies on the flow of ions, and of Na ion in particular, across frog skin have long occupied a prominent place in the biomedical literature. It is well known that both electrochemical and metabolic forces are involved which drive this ion across the epidermis. But the molecular events within the epidermis are largely unknown. Neither is it too clear along which pathways Na positive ions move, since the epidermis presents a network of interconnected compartments which are difficult to approach directly for taking meaningful measurements. In the last few years we have shown that the technique of computer simulation of kinetic data in the literature, when using a multicompartment flow model, is able to consolidate a great number of facts into a coherent picture of flow patterns which are consistent with experimental data. In the next year we plan to continue to apply this technique to data in the literature which, so far, have not yet been subjected to computer simulation. This will include recognition of electrical potential profiles which will be incorporated into the flow model according to new experimental data. In addition, our simulation studies up to this point have allowed us to make several predictions when changing the "initial conditions", relative to the relationships between: rates of transepithelial influx; outflux; cellular vs. extracellular pathways; efficiency of the Na positive negative pump in terms of delta Na ion/delta02. We plan to verify these computer predictions, applying standard laboratory methods to frog skin. BIBLIOGRAPHIC REFERENCES: Huf, E.G. and Howell, J.R. Computer analysis of the Na ion shunt pathways in frog skin epidermis. Comput. a. Biomed. Res. 9, 11-20 (1976). Howell, J.R. and Huf, E.G. Mathematics of non-steady state uptake and release of Na* in a frog skin epidermis model. Comput. in Biol. a. Med. 6, 121-131 (1976).